Electric motors having electro-dynamic braking systems, with our without specific windings, in power tools and appliances are already known. In some tools, such as circular saws, normal unbraked stopping time may be inconveniently long due to the inertia of the motor armature and functional elements such as the circular saw blade.
In typical self-excited dynamic braking systems, release of an "on" switch or trigger simultaneously or sequentially interrupts the flow of electrical power to the tool and effects a reverse of polarity in the windings so that, with the aid of the residual magnetic field in the stator, a self-excited electromagnetic field of force is generated, opposing continued rotation of the motor armature in the original running direction, so that rotation is arrested more quickly than by normal windage and friction.
However, this system only functions if a residual flux level remains in the stator's field. If no residual flux level remains, the self-excited electromagnetic field will not be generated. Braking is then effected by normal windage and friction.
It is an object of this invention to provide an apparatus that guarantees a residual flux level in the stator's field.